The very large expansion of radiotelephones is well known, and those radiotelephones are naturally fitted with their own antennas and they are powered by batteries, optionally rechargeable batteries.
When the user of a radiotelephone is in a motor vehicle, it is advantageous to be able to connect the radiotelephone to the circuits of the motor vehicle, and mainly to an antenna of the vehicle so as to provide better quality of both-way transmission between the radiotelephone and the outside.
For this purpose, the radiotelephone is fitted with a connection element comprising a base, and the motor vehicle is fitted with a connection element comprising a plug which is connected to the antenna of the vehicle. It will be understood that when the radiotelephone is used in independent manner, it is necessary for the radiotelephone's own antenna to be connected to the processor circuits of the radiotelephone, and that when the radiotelephone is connected to the motor vehicle antenna, it is necessary for the link with the radiotelephone's own antenna to be interrupted and for a link to be established between the processor circuits internal to the radiotelephone and the antenna of the motor vehicle.
In order to optimize operation of the radiotelephone when connected to the motor vehicle antenna, it is also desirable for the radiotelephone's own antenna to be connected to radiotelephone ground.
Nevertheless, a connection device with built-in switching can also be used in contexts other than that described above, insofar as a connection is to be made either between a coaxial cable and the circuits of a portable appliance, or a connection is to be made between the same processing circuits of the portable appliance and an antenna belonging thereto.